I. Field of the Invention
This invention relates to leads used in conjunction with cardiac rhythm management devices. More particularly, the present invention relates to the surface electrodes for such leads and a technique for reducing the length of such electrodes while at the same time providing an effective bond between the electrode and adjoining electrically insulative material.
II. Description of the Prior Art
Over the past thirty years, a variety of leads have been developed for use in conjunction with either an implantable heart pacemaker or implantable heart defibrillator. Such leads typically include one or more elongated conductors surrounded by an insulative body, and one or more electrodes coupled to the conductors. The conductors and electrodes provide an electrical path for signals from the heart and delivery of pulses to the heart.
Over the years, a variety of leads have been developed which include one or more ring electrodes. Most often, the ring electrode is a metal band which surrounds the insulative body of the lead. An orifice in the lead body beneath the ring electrode allows the ring electrode to be coupled to a conductor within the lead body.
Recently, "over the wire" leads have been developed.
These leads have been given this name because they are implanted by sliding them over a guidewire. In addition to the conductor, insulative body and electrode, these leads have a central lumen which permits the lead to be passed over the guidewire.
More recently, there has been a need to create leads having smaller cross-sectional diameters. This is true, for example, of leads designed to apply stimulating pulses to the left ventricle without residing in the left ventricle. To be successfully implanted, such leads must pass through the superior vena cava, the right atrium, and the coronary sinus into the great vein of the heart so that the electrode resides in a branch of the coronary vein. This is a tricky path which is best navigated by first using a guidewire and then sliding the lead over the guidewire.
Traditional ring electrodes tend to be relatively long and inflexable. To improve the overall flexability of the lead and thus make it easier to steer, there is a need to reduce the overall length of the electrode. This must be done, however, in a fashion that does not weaken the joints which exists on the proximal and distal ends of the electrode between the edges of the electrode and the electrically insulative body of the lead.
Larger diameter leads have proven to be strong and durable. However, as the diameter is reduced strength can be lost. This is particularly true when ring electrodes are used and joints are formed between the ring electrode and in the insulative body. The joints cause potential weak spots in the lead. Thus, there is a real need to eliminate these weak spots or at least increase the strength of the lead at the interface between the insulative body and the ring electrode. More specifically, there is a real need for a lead having an interface between a ring electrode and insulative body strong enough to handle any axial loading which may be imparted during insertion or removal of the lead.